1. Filed of the Invention
This invention relates to a charge-reducing film to be used in a container containing electron-emitting devices and to an image-forming apparatus comprising electron-emitting devices, an image-forming member and spacers. It also relates to a method of manufacturing such an image-forming apparatus.
2. Related Background Art
Flat panel displays are attracting attention as they save space and are lightweight and hence expected to eventually replace CRT displays. Currently available flat panel displays include the liquid crystal display type, the plasma emission type and the type that utilizes multiple electron sources. Plasma emission type and multiple electron source type displays provide a large visual angle and can display high quality images comparable to those displayed by CRT displays.
FIG. 15 of the accompanying drawings shows a schematic cross sectional view of a display apparatus comprising a large number of minute electron sources. It specifically comprises electron sources 51 formed on a glass rear plate 52, a glass face plate 54 on which fluorescent members 55 are arranged and a support frame 53 airtightly bonded to the outer peripheries of the rear and face plates for supporting them and providing an envelope for the display that secures a vacuum condition in the inside. The electron sources typically comprise so many cold cathode type electron-emitting devices such as field emission type electron-emitting devices having a conical or needle-like tip adapted to field emission of electrons or surface-conduction electron-emitting devices because these devices can be arranged highly densely within a limited surface area. When the display has a large display screen, however, the rear plate and the face plate have to be made very thick in order to make them withstand the pressure difference between the external atmospheric pressure and the internal vacuum of the envelope. Such a display is very heavy and, at the same time, can show distorted images if viewed aslant relative to the display screen. Therefore, there have been proposed various support structures that are referred to as spacers or ribs and designed to be arranged between the rear plate and the face plate in order to make the glass plates of the display withstand the pressure difference between the outside and the inside of the envelope if they are relatively thin. The rear plate on which electron sources are arranged and the face plate carrying thereon fluorescent members are typically separated by a distance between less than a millimeter and several millimeters and the inside of the envelope is held to an elevated degree of vacuum.
Then, a voltage as high as hundreds of volts is applied between the electron sources and the fluorescent members by way of an anode (metal back) (not shown) in order to accelerate the electrons emitted from the electron sources. In other words, an electric field stronger than 1 kV/mm is applied between the fluorescent members and the electron sources so that, if spacers are used, they can give rise to electric discharges on their part. Additionally, the spacers can become electrically charged as electrons emitted from the electron sources located close to them hit them and cations ionized by emitted electrons adhere them, if partly. Then, electrically charged spacers divert the courses of nearby electrons emitted from the electron sources to make them miss the respective targets of fluorescent members so that the viewer will see a distorted image on the display screen behind the front glass plate.
There have been proposed techniques for eliminating electric charges of spacers by causing a weak electric current to flow through them (Japanese Patent Application Laid-Open Nos. 57-118355 and 61-124031). According to such a known technique, a high resistance thin film is formed on the surface of each insulating spacer so that a weak electric current may flow through the surface. Such a charge-reducing thin film is typically made of tin oxide, a crystalline mixture of tin oxide and indium oxide or metal.
A tin oxide thin film is highly sensitive to gaseous substances such as oxygen and hence often used in gas sensors. In other words, it can change its electric resistance if exposed to the atmosphere. Additionally, a thin film made of any of the above listed materials shows a low specific resistance and, therefore, a charge-reducing film layer may have to be formed with islands or it may have to be made extremely thin in order to make it electrically highly resistive.
In short, known techniques of forming an electrically highly resistive film are accompanied by drawbacks, including poor reproducibility and fluctuations in the resistance of the thin film that occur, particularly in some of the steps for manufacturing a display that involve the use of heat, such as the step of sealing the envelope by means of frit glass and that of baking the display (or heating the display while evacuating the inside of the envelope of the display).
In view of the above identified problems, it is therefore a principal object of the present invention to provide a charge-reducing film adapted to reduce the electric charge of a container containing electron-emitting devices. Another object of the present invention is to provide a thermally stable charge-reducing film.
Still another object of the present invention is to provide a charge-reducing film that can minimize the adverse effects of electric charge on emitted electrons.
A further object of the present invention is to provide an image-forming apparatus comprising spacers adapted to reduce the electric charge thereof.
A further object of the present invention is to provide an image-forming apparatus comprising thermally stable spacers.
A still further object of the present invention is to provide an image-forming apparatus comprising an image-forming member and spacers and adapted to minimize the adverse effects of electric charge on emitted electrons and also diversions of the courses of electrons emitted toward the image-forming member.
According to an aspect of the invention, there is provided a charge-reducing film characterized by comprising a nitrogen compound containing a transition metal and aluminum, silicon or boron.
According to another aspect of the invention, there is provided a charge-reducing film characterized by comprising a nitrogen compound containing a transition metal and aluminum, silicon or boron and the nitride ratio of said aluminum, silicon or boron is not less than 60%.
According to another aspect of the invention, there is provided a charge-reducing film characterized by comprising a film of a nitrogen compound containing a transition metal and aluminum, silicon or boron and an oxide layer arranged on the surface thereon.
According to still another aspect of the invention, there is provided a charge-reducing film characterized by comprising a film of a nitrogen compound containing a transition metal and aluminum, silicon or boron, the nitride ratio of said aluminum, silicon or boron being not less than 60%, and an oxide layer arranged on the surface thereof.
According to a further aspect of the invention, there is provided an image-forming apparatus comprising electron-emitting devices, an image-forming member and spacers arranged in an envelope, characterized in that each of said spacers comprises a substrate and any of the above defined charge-reducing films formed thereon.
According to a still further aspect of the invention, there is provided a method of manufacturing an image-forming apparatus comprising electron-emitting devices, an image-forming member and spacers, characterized by comprising steps of preparing spacers by coating substrates with any of the above defined charge-reducing films and arranging the spacers, electron-emitting devices and an image-forming member in an envelope and thereafter hermetically sealing the envelope, keeping, if necessary, a non-oxidizing atmosphere within the envelope.